Consider the use of two or more tires mounted at each end of a vehicle's axle. This is a common procedure with vehicles carrying heavy loads in order to maintain road pressure below limits. Even if the pressure inside each tire is initially the same, there is a tendency for the inside pressures to diverge as the vehicle travels down the road. This occurs because one tire will effectively have somewhat more load than the others (perhaps because it is slightly larger or is less able to reject heat) resulting in it becoming hotter than the others, resulting in an internal pressure that is higher, resulting in it becoming a bit larger, resulting in it taking on somewhat more load, and so on until either an equilibrium is reached or the tire is destroyed. Even if equilibrium is achieved, the result is an uneven load distribution between the tires and unequal service lives. What is desired is for each tire to shoulder an essentially equal amount of the load. Assuming similar tires, this desired state occurs, or is close to occurring, when the inside pressures of the tires are equal.
One could run a conduit between the tires so that an increased pressure in one tire would cause air to flow into the other tires and inherently equalize all of their pressures while allowing the pressurization from an external source through a spur to the conduit. A similar device may be described in U.S. Pat. No. 3,302,682. Such a device causes all connected tires to go flat if one goes flat.
A number of devices have used a pressure sensitive means to interpose a single barrier between ports communicating with tires such that the tires are isolated when the pressure in one tire becomes less than a certain amount. Such isolating devices may be described in U.S. Pat. Nos. 3,468,162, 3,760,859, 4,203,467, and 4,539,928. These devices tend to be complicated and expensive to construct. If the single pressure sensitive barrier fails, the entire system fails.
Accordingly, an object of the present invention is a relatively inexpensive, reliable device (using simple or conventional parts) that maintains an equal pressure in each tire as long as that pressure is above an adjustable, threshold amount and that isolates the tires when the pressure attempts to go below the threshold.
More particular objects of the present invention are/is a device that facilitates pressurizing the tires from one port, monitoring the pressure from one port, and a device such that the failure of one valve or diaphragm will not cause a catastrophic failure of the system.